The fact is that the cryptocurrency market has been considered more stable for a long period than it was a few years ago. Based on this, it would be a big mistake to think that the bull run will end very quickly. I believe that the bullish trend will continue not only until the end of 2021, but also next year.
last year the movement of bitcoin was due to the influence of @elonmusk and it was clear, when entering 2021 there was a slight correction and it didn't happen like 2018, which indicated that the @elonmusk effect was clearly felt. to note that this year should be the halving effect will occur, then the price is still moving.
The halving is expected to occur at the end of the year, so you can imagine the effect. just now the price is high enough, so many experts predict that the price of bitcoin will increase very sharply. but indeed altcoins will be left behind if bitcoin does not experience correction and price stability, for that it requires bitcoin price stability so that altcoins can move first to reach ATH.
whether there will be an increase until next year as you say, all depends on the conditions at the beginning of the year which usually will be corrected, if the correction is too deep then the movement will stop.